Phototube with electron multiplier



Dec 31, 1940- K. scHLEsxNGER PHOTOTUBE WITH ELECTRON MULTIPLIER Filed Feb. 19, 1938 2 Sheets-Sheerl 1 ...AAA

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INVENTOR KURT scf/Es/NGER AAAA AAAAAAA AAAAAAAA AAAAA vvvvvvvvvvzvvvvvvvvvvvvvvvv ATTORNEY Filed Feb. 19, 1958 2 Sheets-Sheet 2 lNVENTOR n 6 W w M. C S .m U K Y E N R O T T A Patented Dec. 31, 1940A rHoTo'rUE WITH EIiEcTRoN MULTIPLIER Kurt Schlesinger, Berlin,

Germany, assigner, by

` mesne assignments, to Loewe Radio, Inc., acorporation of New York Application February 19, 13s,s`erial-N0.191,451 v vIn Germany February241937 l I c 'claims (01.250-275),` ,y

More recently the electron multipliers according to Weiss, the so-called net ampliers, have acquired considerable practical signicance. Generally it is desired to have in a tube of this kind, shown in Fig. 1, a photo-cathode I which is as large as possible. Accordingly therst of the amplifying nets 2|-23 must also have a large surface, as the emitted electrons are rather undirected. In order now to prevent the electrons flying through the nets from breaking away from the axis of the system the applicant has already set forth some time ago in U. S. A. application Ser. No. 122,032 dated January 23, 1937, and Ser. No. 171,898 dated October 30, 1937, that concentration cylinders 3|-33 should be provided, each cylinder being electrically connected with the preceding net, both sets of electrodes being furnished with increasing potentials by a potentiometer 4. In this case each stage is equal to the preceding one.

Since the cross-section of the bundle of cathode rays does not converge in an arrangement of this character, the linal collector electrode 5 must have substantially the same large crosssection as the initial net 2|. In this there is a disadvantage immediately an electron multiplier of this nature requires to be connected to an amplifying tube. The large-surface collector net 5 has a rather large capacity, and the resistance 6 coupling the tube with the ampliiler grid must accordingly be so small that the adaptation to the tube is poor. If the collector 5 could be made considerably smaller, resistance 6 and consequently the useful potential could be considerably increased. 'I'his would be possible if it could be accomplished that the cross-section of the bundle of electrons contracts more and more upon traversing the net amplier.

This object is accomplished by the tube according to Fig. 2. The concentration cylinders 5 |-53 possess the same potential, viz., the most negative potential of the system being connected with the cathode They have, as well as the nets 4| to 43 decreasing diameters. In place of separate graduated cylinders there can then also be used, in accordance with Fig. 3, an integral metallic funnel 3. 'I'he funnel form produces particularly favourable conditions, although it is also possible in itself to make this electrode cylindrical.

It is, therefore, also always possible to employ a very small collector electrode 5, irrespective of the size which the photo-cathode I may require to be. In the case of larger initial areas 4|, it

ismerely necessary to increase the length of the system. l

This consideration has been coniirmed in practice within the accuracy limits to be demanded, it being shown that a contraction of the diame- 5 ter to one-half can be accomplished with a multiplying system having a length of approximately 50 mm. Thus, for example, an initial net of 40 mm. in diameter could be .combined Without loss with a collector 5 of 20 mm. diameter. 10

The collecting electrode 8 may, according to Fig. 3, advantageously be replaced by` a fourpole cylindrical collector, performing in itself an additional multiplication by secondary emission as described in my application Ser. No. 190,003.

A collector of this kind consists of a semi-cylindrical net 8, an electrode 9 forming the other half of the cylinder,`a pin electrode I0 in the axis of the system and a cylindrical grid surrounding said pin. The potentials of said 4 electrodes are 20 tapped at the potentiometer 4.

I claim:

l. An electron multiplier comprising a large surface cathode, a series of plane surface secondary emissive nets mounted substantially parallel 25 with one another and perpendicular to the axis of said multiplier and adapted toV be provided with stagewise increasing positive potentials with respect to said cathode, a .collecting anode, and electron-optical means between said cathode and 30 said anode for gradually reducing the diameter of the electron stream along its path between said last mentioned electrodes, said nets having stagewise decreasing diameters in the direction from said cathode towards said anode.

2. An electron multiplier comprising a large surface cathode, a series of plane surface secondary emissive nets mounted substantially parallel with one another and perpendicular to the axis of said multiplier and adapted to be provided 40 with stagewise increasing positive potentials with respect to said cathode, a series of cylindrical electrodes each being disposed between two adjacent ones of said nets and connected to said cathode, and a collecting anode.

3. An electron multiplier comprising a large surface cathode, a series of plane surface secondary emissive nets mounted substantially parallel with one another and perpendicular to the axis of said multiplier and adapted to be provided with 50 stagewise increasing positive potentials with respect to said cathode, a collecting anode, and a cylindrical electrode surrounding said nets and connected to said cathode.

4. An electron multiplier comprising a large 55 surface cathode, a series of plane surface secondary emissive nets mounted substantially parallel with one another and perpendicular to the axis of said multiplier and adapted to be provided with stagewise increasing positive potentials with respect to said cathode, a series of cylindrical electrodes each being disposed between two adjacent ones of said net and connected to said cathode, and a collecting anode, said nets as well as said cylindrical electrodes having stage-Wise decreas-l ing diameters in the direction from said cathode towards said anode.

5. An electron multiplier comprising a large surface cathode, a series of plane surface secondary emissive nets mounted substantially parallel with one another and perpendicular to the axis of said multiplier and adapted to be provided-with stage-Wise increasing positive potentialsl with respect to said cathode, a collecting anode, and a funnel-shaped electrode surrounding said nets at about equal distances therefrom and being connected to said cathode, said nets having stage- Wise decreasing diameters in the direction from said cathode towards said anode.

6. An electron multiplier comprising a large surface cathode, a series of plane surface secondary emissive nets mounted substantially parallel with one another and perpendicular to the axis of said multiplier and adapted to be provided with stage-wise increasing positive potentials with respect to said cathode, a funnel-shaped electrode mounted inside said multiplier surrounding said nets and connected to said cathode, and a collecting system consisting of a further net-shaped electrode having the shape of one half of a cylinder, a further solid electrode forming the other half of said cylinder, a pin electrode forming the axis of said cylinder and being mounted perpendicular to the axis of said multiplier, and a gridlike output electrode mounted between said pin electrode and said cylinder. Y f

KURT SCHLESINGER. 

